This invention relates to an optical recording/reproducing apparatus and more particularly, to a magnetooptic recording/reproducing apparatus which records or reproduces an information signal by a laser beam onto or from a rotating magnetooptic disc.
In the magnetooptic recording/reproducing apparatus of this type, there exists an optimal intensity (power) of a recording laser beam which is determined in accordance with a characteristic of an applied disc, and therefore it is significant to find the optimal laser power. One of the prior art techniques to learn an optimal laser power is to find the power experimentally in advance. Another prior approach is to employ recording and reproducing laser beams which are arranged to read out an information signal immediately after recording to evaluate the quality of the read out information signal and, thus, to control the power of the recording laser beam at an optimal level in a feedback manner. (See, for example, Japanese Open-Laid Patent 63-56822.)
However, the former approach is not practical because an optimal laser power differs disc by disc and discs have some aging characteristics. This technique is especially impractical in applying to the apparatus which rotates a magnetooptic disc at a given angular speed for recording/reproducing so that the line velocity is varied between an inner side track and an outer side track on a disc due to difference in radial distance because a received laser power level on the disc changes with a change in radial distance. The drawback of the latter technique, although it can achieve the optimal laser beam power succesively, is to require an optical head which can emit the recording and reproducing laser beams simultaneously, together with complicated arithmetic processing, resulting in pushing up the production cost.